Processes for preparing impressions of human and animal teeth have been described in German Patent Application No. 2,249,822. According to the process described in this German Patent Application, a composition containing (a) a diorganopolysiloxane having as terminal units triorganosiloxy groups each of which contains at least one vinyl group, i.e., an organopolysiloxane having at least two alkenyl groups per molecule, (b) an organopolysiloxane having at least 3 Si-bonded hydrogen atoms per molecule, (c) a catalyst which promotes the addition of Si-bonded hydrogen to alkenyl groups, and (d) up to 90 percent by weight of a filler, based on the total weight of the composition, is crosslinked while in contact with the surface of which an impression is to be taken, and thereafter the formed structure is removed from the surface of which the impression was taken.
When the process described in the German Patent Application is employed to obtain an impression simultaneously of more than one tooth, it was necessary to use a composition, such as an alginate, in order to obtain an impression whose inside diameter is greater than that of the final impression because the Shore-A hardness of the crosslinked products described in the German Patent Application is so low. Also, the use of a composition such as an alginate in making these impressions was very objectionable from a physiological point of view. From this first impression, it was necessary to prepare a positive from, for example gypsum and to use the positive to prepare a so-called impression spoon. Up to the present time, the material used for the impression spoon consisted of, for example, polyester or polymethyl acrylate. Then the impression spoon and a composition prepared in accordance with German Patent Application No. 2,249,822 were used to make the final impression. All of these steps are time consuming and expensive. Thus one of the advantages of this invention is that the compositions form impressions having a higher Shore-A hardness value and these compositions can be used for taking simultaneous impressions of more than one tooth even in the absence of an impression spoon and, generally, obtain impressions in the absence of stiffening agents or lining materials, i.e,, materials which compensate for the difference in the dimensions of the some-what larger impression and the actual dimensions of the tooth.
An added advantage of the process of this invention is when simultaneous impressions are taken of more than one tooth, there is no need to use an alginate, since the process of this invention makes it possible to obtain an impression whose inside dimensions are larger than those of the final impression and the first impression obtained from the process of this invention can be used to prepare a positive and an impression spoon from still another material with the aid of said positive, which itself can be used as an impression spoon. The impression spoon can accept the composition used in the preparation of the final impression; for example a composition of the type described in German Patent Application No. 2,249,822.
The latter application of the process of this invention has the added advantage that the impressions obtained from the crosslinked products prepared from the compositions of German Patent Application No. 2,249,822, adhere substantially better than the heretofore known impression spoons. This avoids the possibility that the final positives might be encumbered by errors which are caused by inadequate adhesion of the final impression on the impression spoon.
Therefore, it is an object of this invention to provide a composition which can be used to make impressions. Another object of this invention is to provide compositions for preparing impressions which have a higher Shore-A hardness. Still another object of this invention is to provide compositions for preparing impressions which have good storage stability. A further object of this invention is to provide a process for preparing impressions simultaneously of more than one tooth.